It is a well-known phenomena that electromagnetic radiation within the near ultraviolet, or "UVA" spectrum of approximately 315 to 400 nanometer wavelength produces fluorescence in certain materials. That is, the fluorescent materials absorb radiated energy at the UVA wavelength and re-radiate it at a longer wavelength in the visible spectrum. This phenomena has enabled inspection and detection techniques in which fluorescent dyes, inks or paints are illuminated by lamps selectively filtered to emit only ultraviolet radiation (often called "black light" because little visible spectrum light escapes the filter), and then re-radiate with a high luminescence in the visible spectrum. These techniques are used extensively in non-destructive testing, leak detection and security systems.
For example, the slow leakage of refrigerant from an air conditioning system is difficult to locate by any other means, because the refrigerant escapes as an invisible gas at such low rate and rapid diffusion that the concentration of refrigerant in air near the leak site is difficult to differentiate from that surrounding any other location along the system circulation lines. However, by infusing into the circulating system a small amount of fluorescent dye which is soluble in the refrigerant, the dye is carried out of the system with the refrigerant, and glows brightly at the leak site when the area is swept with a UVA lamp. A similar procedure can be used to locate leaks of other fluids, such as lubricant oils, fuels, heat transfer fluids or hydraulic fluids. Other UVA inspection techniques use fluorescent dyes or paint to detect fissures or stress cracks in structural members.
Where an inspection for leaks, cracks or fissures is conducted in confined or difficult to reach spaces, it would be advantageous to use a compact, hand-held lamp. It would also be an advantage for maneuverability and for insertion through narrow spaces to have the lamp's handle aligned with the beam direction, as in a traditional in-line flashlight However, a compact lamp must be capable of radiating UVA radiant flux sufficient to produce, at a distance of about eight to thirty inches from the lamp, a fluorescent response in the detector material to re-radiate sufficient lumens to be easily sighted by the inspector.
A compact, hand-held, high intensity ultraviolet inspection lamp has not previously been developed, and apparently has been regarded as impractical, due to the large amount of heat developed by the high intensity source bulbs and the UV filters which are required to produce a sufficient flux of UVA emission from the lamp. As a general proposition, incandescent lamps with higher filament temperatures radiate a greater percentage of light in the ultraviolet range than do cooler filaments. Thus, a high-temperature tungsten halogen lamp is well suited for a UVA light source, but it simultaneously produces much direct heat and visible light radiation. Arc discharge lamps which emit a substantial percentage of ultraviolet radiation, such as mercury vapor lamps and metal halide lamps, also operate at high temperatures.
Moreover, even given that a larger percentage of ultraviolet radiation is emitted from hotter lamps, the light which is radiated from the lamp in the visible spectrum must be blocked from emission by a selective filter, which absorbs and converts visible light into heat while transmitting the ultraviolet radiation.
Thus, there are typically at least two heat sources to consider in designing a compact hand-held UVA lamp; the light source itself and the UV filter. Moreover, the focusing reflector may selectively reflect UV while absorbing visible radiation, becoming a third heat source. If these heat-generating components are located in close proximity to each other in a compact, hand-held lamp, the combined heat is likely to produce unsafe temperatures in the lamp housing, thus creating a potential hazard for severe burns to an operator, or causing components to deform, fracture, or otherwise prematurely fail. Since the compact lamp's handle is located close to the heat-generating components, heat conducting back from the housing to the handle may make the handle uncomfortably hot if the lamp is operated for more than a brief interval.
Despite these difficulties, a compact, high intensity UVA inspection lamp would have great appeal to several industries which use UVA light in maintenance or inspection processes. Contemporary UVA lamps of sufficient power to be considered high intensity tend to incorporate large bulbs, external heat guards, bulky bulb housings, and pistol-type handles which are off-set from the beam direction. These large lamp assemblies can absorb and dissipate internal heat over a considerable surface area of the lamp assembly, thereby producing relatively mild temperatures on the external surfaces.
These larger UV lamps tend to obstruct the users'view of the components being inspected, and their size may prevent the user from bringing the lamp close to components of complicated machinery or from inserting it into areas which are difficult to reach. This can limit the effectiveness of a UVA inspection.
Accordingly, there is a need for a compact, in-line, hand-held UVA inspection lamp that can be used in tight spaces and maneuvered to illuminate the parts to be inspected. This compact UVA light source must have sufficient UVA emission, yet be capable of dissipating the heat generated by producing that UVA emission without creating discomfort or hazard to operators, or failure of its component parts. It is an object of this invention to provide a lamp having this capability.